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Set font scale

set_font_scale

Set text size on Android and iOS for accessibility testing. Pass a scale like 1.0 or 2.0; Android applies directly, iOS maps to Dynamic Type.

Instructions

Set text size for accessibility testing. scale 1.0 = default. Android sets font_scale directly; iOS maps to the nearest Dynamic Type size.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "device_id": "<device_id>",
      "scale": "<scale>"
    },
    "name": "set_font_scale"
  }
}

Input Schema

Name	Required	Description	Default
`scale`	Yes	e.g. 0.85, 1.0, 1.3, 2.0
`device_id`	Yes	Device id from list_devices (adb serial like 'emulator-5554', or an iOS simulator UDID)

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.2.0Jul 31, 2026

TDQS

A4.4/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description must carry all behavioral disclosure. It does this well by revealing platform-specific behavior: 'Android sets font_scale directly; iOS maps to the nearest Dynamic Type size.' It also clarifies default scale. However, it does not touch on side effects like persistence or app restart requirements, so a 4 is appropriate.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is exactly two sentences, leads with the core purpose, and then packs essential behavioral details without any wasted words. Every sentence earns its place.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a simple setter with two parameters and no output schema, this description covers the purpose, default scale, and platform behavior comprehensively. It lacks explicit return/error info, but for this operation that is not critical. Overall, it is complete enough for an agent to understand the tool's function and key behaviors.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% with descriptions for both parameters, so baseline is 3. The description adds extra meaning by explaining 'scale 1.0 = default' and the platform mapping nuance, which enriches understanding of the 'scale' parameter beyond the schema's examples. This warrants a 4.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the verb 'Set' and the specific resource 'text size for accessibility testing', which immediately distinguishes this from sibling tools like set_appearance or set_locale. It precisely conveys the tool's function without ambiguity.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The phrase 'for accessibility testing' provides a clear context for when to use this tool, but it does not explicitly mention when not to use it or suggest alternatives. This is adequate context without exclusions, hence a 4.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.